1. Field of the Invention
The present invention relates to semiconductor integrated circuit manufacturing and, more particularly to a method of forming a conformal amorphous carbon layer suitable for etching processes and double patterning processes.
2. Description of the Related Art
Integrated circuits fabricated on semiconductor substrates for large scale integration require multiple levels of metal interconnections to electrically interconnect the discrete layers of semiconductor devices on the semiconductor chips. The different levels of interconnections are separated by various insulating or dielectric layers, which have been etched via holes to connect one level of metal to the next.
The evolution of chip design continually requires faster circuitry and greater circuit density. The demands for faster circuits with greater circuit densities impose corresponding demands on the materials used to fabricate such integrated circuits. In particular, as the dimensions of integrated circuit components are reduced to the sub-micron scale, the demands for greater integrated circuit densities also impose demands on the process sequences used in the manufacture of integrated circuit components. For example, in process sequences that use conventional photo lithographic techniques, a layer of energy-sensitive resist is formed over a stack of material layers disposed on a substrate.
As the pattern dimensions are reduced, the thickness of the energy-sensitive resist must correspondingly be reduced in order to control pattern resolution. Such thin resist layers can be insufficient to mask underlying material layers during the pattern transfer step due to attack by the chemical etchant.
Recently, Amorphous hydrogenated carbon is widely used as hardmask material between the energy-sensitive resist layer and the underlying material layers to facilitate pattern transfer because of its good etch selectivity relative to silicon dioxide or silicon nitride, optical transparency, and good mechanical properties. However, current deposition processes for amorphous carbon hardmask result in poor step coverage and/or non-conformal sidewall protection of the hardmask on the uneven surface of the substrate making successful pattern transfer increasingly difficult as pattern densities continue to shrink.
If pre-etch critical dimension of the pattern is out of specification after photo-lithography, a rework process may be performed to remove the resist layer from the substrate and re-pattern the substrate with a new resist layer. During rework process, the surface of the underlying layer, amorphous carbon hardmask layer, may be attacked by the etchant used to remove the resist mask, thereby causing thickness of the hardmask to be reduced or the profile of the hardmask to be undercut.
The hardmask thickness loss or undercut profile associated with the rework process changes the uniformity and/or step coverage of the new resist layer formed over the hardmask layer, thereby contributing to inaccurate transfer of the desired pattern to the film stack, which may adversely influence subsequent processes used for interconnect formation and disadvantageously impact the overall electrical performance of the device.
In addition, for advanced lithography, the ability to pattern not only small pitches, but also small critical dimensions (CDs), is very important. For front-end applications, patterns may be narrowed after lithography development through the use of trim techniques during the subsequent etches process. For back-end applications, shrink techniques are needed to reduce trenches and contacts to the required narrow critical dimensions. The conformal deposition, using plasma enhanced chemical vapor deposition system, is a post-lithography process that covers the top and sidewalls of the photoresist with an amorphous carbon layer. This amorphous carbon layer has a high etch resistance for subsequent etch steps and can be removed with standard ash processes afterwards.